[meteorite-list] Martian Scars (Mars Express)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 Oct 2013 13:15:07 -0700 (PDT)
Message-ID: <201310102015.r9AKF7Hn005718_at_zagami.jpl.nasa.gov>

http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Martian_scars

Martian scars
European Space Agency
10 October 2013

Ripped apart by tectonic forces, Hebes Chasma and its neighbouring
network of canyons bear the scars of the Red Planet's early history.

ESA's Mars Express has flown over this region of Mars on numerous
occasions, but this new eight-image mosaic reveals Hebes Chasma in
full and in greater detail than ever (click image for full mosaic).

[Image]
Hebes Chasma in context

Hebes Chasma is an enclosed, almost 8 km-deep trough stretching
315 km in an east-west direction and 125 km from north to south at
its widest point. It sits about 300 km north of the vast Valles
Marineris canyon complex.

The origin of Hebes Chasma and neighbouring canyons is associated
with the nearby volcanic Tharsis Region, home to the largest
volcano in the Solar System, Olympus Mons.

[Image]
Hebes Chasma topography

As the Tharsis bulge swelled with magma during the planet's first
billion years, the surrounding crust was stretched, eventually
ripping apart and collapsing into gigantic troughs, including
Hebes Chasma. Intricate fault patterns can be seen all around the
deep depression - they are especially evident in the main colour
and 3D images.

In the centre of Hebes Chasma, there is a flat-topped "mesa" that
rises to level similar to that of the surrounding plains. It is
shown from different angles in the two perspective images below.

No other canyon on Mars has a similar feature and its origin is
not entirely clear. Its layers include volcanic materials - just
like in the main canyon walls - but also wind-blow dust and lake
sediments that were laid down over time.

A horseshoe-shaped chunk has been taken out of one side of the
mesa, seen below, where material has slumped down onto the valley
floor below.

[Image]
Hebes Chasma in 3D

A landslide may also be responsible for the dark patch in this
image, which appears to pool like spilt ink across the debris. It
is most likely loose dust that has slid down the walls, perhaps
helped along where melting ice or ground-water weakened the rocks
to create a flow-like feature. A similar feature is visible at the
opposite end of the mound, as seen in the full-colour image.

Other landslide deposits are seen all over the floor of Hebes
Chasma, many coming from the main canyon walls. Numerous grooves
are etched into both the canyon walls and the mesa, suggesting the
material is weak and easily eroded.

[Image]
Landslides and rock layers inside Hebes Chasma

In the second perspective view above, a thin band of darker
material is seen between two layers of light material. One idea is
that the material was blown or slid from the top of the mound and
collected on the slopes below. Dark material is also seen around
the base of the mesa, which either eroded away from the younger
sediment layers located higher up in the mesa, or were deposited
separately by wind or water.

Other layers revealed in the sides of the mesa may also have been
deposited by water. Data from both Mars Express and NASA's Mars
Reconnaissance Orbiter reveal that some parts of Hebes Chasma are
laced with minerals that can form only in the presence of water,
suggesting that at some point in the Red Planet's history the
canyon might have been filled with a lake.

However, it is apparent from the chaotic debris that fills the
canyon floor that enormous landslides have also played a key role
in shaping and widening this deep scar since its formation.

[Image]
Hebes Chasma in 3D
Received on Thu 10 Oct 2013 04:15:07 PM PDT